The present invention generally relates to a display device, and more specifically to a light emitting diode (LED) display having high resolution and brightness and the method of manufacturing the same.
The recent advance in computers, personal communication devices and various information appliances has brought a new industrial revolution into human history. These electronic devices have changed and transformed human life significantly. Almost every one of these devices requires a display to show input and output information. Many researchers and manufactures are striving to develop or invent new display devices with high resolution, rich colors, wide viewing angles and high brightness along with small volumes and light weight.
Conventionally, cathode ray tubes (CRT) are the most popular display devices widely used in a television or a computer. Although a CRT has many advantages as a display device, its bulky size and heavy weight have made it very inconvenient or even impossible to be a part of a compact and portable electronic device. In recent years, flat panel liquid crystal display devices have been used widely in a notebook or a personal communication device. Other flat panel display devices such as plasma displays and field emission displays are also being developed and finding their market places.
LEDs represent another type of device that has a great potential to be used as a light weight and high quality display devices. However, because many difficulties in full-color LED display technology remain to be overcome, LED devices generally are used only as traffic or vehicle lamps for illumination. Some advertisement or bulletin board also uses LEDs as a display device for showing simple messages.
In the state of the art semiconductor technology, an LED device typically is fabricated with an active layer between upper and lower cladding layers on top of a semiconductor substrate. The composition of semiconductor materials chosen in these layers determines the color of the LED device. LED layers of different materials for different colors can only be grown or deposited on appropriate substrates. Because a semiconductor substrate typically is appropriate for forming two LEDs emitting light having closer spectra, such as red and green LEDs or green and blue LEDs, the third LED has to be formed on a different substrate in order to fabricate a full-color LED device.
Consequently, although LEDs of red and green colors may be fabricated on a same substrate, fabricating a blue LED on the very same substrate has been difficult. LED displays of full-color is yet to be developed. If a full-color LED display can be successfully manufactured, it has many advantages such as wide viewing angle, small volume and light weight. Therefore, there is a strong need in developing a full-color, high resolution and brightness LED display.
This invention has been made to meet the need of a full-color, high resolution and brightness LED display. The primary object is to provide a new structure for a full-color LED device. It is also an object of the invention to provide a method of fabricating the full-color LED device. It is yet another object to provide a full-color LED display by means of a plurality of full-color LED devices. A full-color LED display requires the fabrication of red, green and blue LED elements in a semiconductor device structure. This invention uses wafer bonding and chemical-mechanical polishing technique to provide more than one substrate for forming LEDs of red, green and blue colors on a same display.
According to the invention, a first semiconductor substrate for manufacturing an LED element of a first color is first prepared. A first color LED element is fabricated on a buffer layer that covers the semiconductor substrate. In general, a second color LED element can also be fabricated on the same substrate adjacent to the first color LED element. A first passivation layer is then formed above the buffer layer and the two LED elements. A second semiconductor substrate is then bonded to the first passivation layer and polished as a thin substrate layer by chemical-mechanical polishing (CMP). An LED element of a third color is subsequently fabricated above the second substrate. A second passivation layer is deposited above the semiconductor device structure that comprises the three LED elements. Thus, a full-color LED device is fabricated.
The order of forming red, green and blue color LED elements is not critical in this invention. Dependent on the semiconductor substrates chosen, the second color LED element may be formed on the first or second substrate. In general, red and green LED elements may be formed on a same substrate, and green and blue LED elements may also be formed on a same substrate. However, it is difficult to form red and blue LED elements on a same substrate.
A full-color LED display can be manufactured by arranging a plurality of full-color LED devices in rows and columns in a matrix form. By providing proper metal lines and electrode layers along with peripheral circuits, each full-color LED device can be addressed and controlled to display a full-color image.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.